Microelectromechanical systems (MEMS) integrate electrical and mechanical devices on the same silicon substrate using microfabrication technologies. The electrical components are fabricated using integrated circuit processes, while the mechanical components are fabricated using micromachining processes that are compatible with the integrated circuit processes. This combination makes it possible to fabricate an entire system on a chip using standard manufacturing processes.
One common application of MEMS is the design and manufacture of sensor devices. The electro-mechanical portion of the device provides the sensing capability, while the electronic portion processes the information obtained by the electro-mechanical portion. One example of a MEMS sensor is a MEMS gyroscope.
A type of MEMS gyroscope uses a vibrating element to sense angular rate through the detection of a Coriolis acceleration. The vibrating element is put into oscillatory motion in the X-axis (drive plane), which is parallel to the substrate. Once the vibrating element is put in motion, it is capable of detecting angular rates induced by the substrate being rotated about the Z-axis (input plane), which is parallel to the substrate. The Coriolis acceleration occurs in the Y-axis (sense plane), which is perpendicular to both the X-axis and the Z-axis. The Coriolis acceleration produces a motion that has an amplitude that is proportional to the angular rotation rate of the substrate.
The dynamic range of an angular rate sensor device is the ratio of the highest sensed rate to the lowest sensed rate. A large dynamic range is usually desirable as long as the resolution of the sensor device is not compromised. The highest sensed angular rate for some MEMS vibratory gyroscopes may be approximately 1000 degrees/second, which limits the dynamic range of the device.
The scale factor of the sensor device is the ratio of the change in output to a unit change of the input. For example, if the scale factor of a MEMS gyroscope is set at 0.0025 volts/degree/second for a MEMS gyroscope with an operating voltage of 2.5 volts, and the angular rate input is 1000 degrees/second, then the output of the MEMS gyroscope will be 2.5 volts. If the highest sensed angular rate for the MEMS vibratory gyroscope is 1000 degrees/second and the angular rate goes above 1000 degrees/second, the output of the MEMS gyroscope will remain at 2.5 volts. There are many applications, such as an Inertial Measurement Unit for smart munitions, which require the MEMS gyroscope to have a larger dynamic range.
Therefore, it would be desirable to increase the dynamic range of a MEMS gyroscope. By adjusting the scale factor of the MEMS gyroscope, the highest sensed angular rate may be increased, thereby increasing the dynamic range of the device.